Such gas measuring devices are known in the form of through-flow testing tubes or also as dosimeters in the form of tubes or badges. The detection of the gas occurs by means of a coloration of an indicator layer which can be in the form of a charge placed in the elongated tube or as a coating of a badge carrier. The gas concentration or gas quantity is observed either by means of a scale placed along the length of the tube or by means of a comparison of the coloring intensity with a predetermined color standard.
Such gas measuring devices in the form of testing tubes are disclosed in U.S. Pat. 3,113,842 and as dosimeter tubes in German published patent application DE-OS 14 98 909.
The known colorimetric gas measuring devices have the disadvantage that they can be only extended to a limited length because of their elongated form and therefore cannot be utilized for making measurements of any desired duration. Also, their sensitivity cannot be increased in an unlimited manner by extending the measuring length. In the case of badge-like measuring devices for determining dosage, a scale for assuring an accurate observation or for a color intensity comparison can only be applied to locations thereon which are unsuitable.